Mechanically freeing wood fibers in the presence of spent peroxide bleaching liquor

Abstract

A process for the preparation of a cellulose pulp by mechanically freeing wood fibers in a grinder to form a fibrous pulp and bleaching the fibrous pulp with a peroxide-containing bleaching agent, as the only bleaching agent, in a peroxide bleaching stage, the mechanical freeing of the fibers being carried out in the presence of a spent liquor from the peroxide bleaching stage have a pH of 7 to 9.

I claim: 
     
       1. In the process for the preparation of a cellulose pulp by mechanically freeing wood fibers in a grinder to form a fibrous pulp, and bleaching the fibrous pulp in a peroxide bleaching stage by adding a peroxide-containing bleaching agent, as the only bleaching agent, to said fibrous pulp the improvement which comprises mechanically freeing the wood fibers in a separate step preliminary to said bleaching, in the presence of only spent bleaching liquor from said peroxide bleaching stage, said liquor having a pH within the range from 7 to 9. 
     
     
       2. The process of claim 1, in which the peroxide-containing bleaching agent is hydrogen peroxide. 
     
     
       3. The process of claim 2, in which the pH of the spent liquor is higher than 7.5. 
     
     
       4. The process of claim 3, in which the pH of the spent liquor is 8 to 9 . 
     
     
       5. The process of claim 1, in which one part of the spent liquor also is added to the fibrous pulp after the grinder but before the addition of the bleaching agent.